A gas turbine used in power generation, etc. is composed of a compressor, a combustor, and a turbine as main members. The gas turbine often has a plurality of combustors, and mixes air, which is compressed by the compressor, with a fuel supplied to the combustors, and burns the mixture in each combustor to generate a high temperature combustion gas. This high temperature combustion gas is supplied to the turbine to drive the turbine rotationally.
An example of the combustor of a conventional gas turbine will be described with reference to FIG. 12.
As shown in FIG. 12, a plurality of combustors 10 of this gas turbine are arranged annularly in a combustor casing 11 (only one combustor is shown in FIG. 12). The combustor casing 11 and a gas turbine casing 12 are full of compressed air to form a casing 13. Air, which has been compressed by a compressor, is introduced into this casing 13. The introduced compressed air enters the interior of the combustor 10 through an air inlet 14 provided in an upstream portion of the combustor 10. In the interior of an inner tube 15 of the combustor 10, a fuel supplied from a fuel nozzle 16 and compressed air are mixed and burned. A combustion gas produced by combustion is passed through a transition pipe 17, and supplied toward a turbine room to rotate a turbine rotor.
FIG. 13 is a perspective view showing the fuel nozzle 16, the inner tube 15, and the transition pipe 17 in a separated state. As shown in this drawing, the fuel nozzle 16 has a plurality of premixing fuel nozzles 16a, and one pilot fuel nozzle 16b. A plurality of swirlers 18 are provided in the inner tube 15. The plurality of premixing fuel nozzles 16a penetrate the swirlers 18, and are then inserted into the inner tube 15.
Thus, the fuel injected from the premixing fuel nozzles 16a is premixed with air, which has been converted to a swirl flow by the swirlers 18, and is burned within the inner tube 15.
The example of FIGS. 12 and 13 is of the type in which the fuel nozzle 16 is inserted into the swirlers 18 provided in the inner tube 15. However, there is also a combustor of the type in which a plurality of swirlers (swirl vanes) are provided on the outer peripheral surface of a fuel nozzle, and a fuel is injected from the swirlers.
With the combustor of the type having the plurality of swirlers (swirl vanes) provided on the outer peripheral surface of the fuel nozzle, lean premixed combustion is adopted as a technique for raising the efficiency of the gas turbine while decreasing the generation of CO and UHC. If such lean premixed combustion is employed, the mixture ratio of fuel and air (fuel-air ratio: F/A) has to be maintained in “a specific range” in order to suppress the generation of CO and the generation of UHC at the same time.
Patent Document 1: Japanese Unexamined Patent Publication No. 1999-14055
Patent Document 2: Japanese Unexamined Patent Publication No. 2004-12039